RELAX – Crustal relaxation below large impact craters inferred from novel imaging of analogue experiments
Final Report Abstract
The aim of the project was to address an important knowledge gap in planetary geology by better understanding long-term crater modification, one of the most common tectonic processes in the Solar System. In this regard, two mechanisms have been proposed to explain the formation of floor-fractured craters: emplacement of horizontal igneous sheets beneath the crater floor and isostatic re-equilibration of crust underlying the crater floor. Using scaled analogue experiments, we systematically investigated the structural consequences of both mechanisms on long-term crater floor deformation. The results of the physical modelling allowed us to quantify the evolution, kinematics and pattern of crater-floor fractures. Most importantly, the analogue experiments provided, for the first time, a quantitative relationship between the diameter, depth and fracture geometry of crater floors with regard to crustal thickness and depth of horizontal igneous sheets below lunar craters. As the majority of natural lunar craters is dominated by polygonal fractures, the emplacement of sills occurs likely at shallow crustal levels. Evacuation of (model) igneous sheets provides an explanation for the ubiquitous presence of downfaulted terraces observed at lunar crater margins. Horizontal crustal flow towards the crater centre is an intrinsic mechanism during long-term isostatic reequilibration of crust. Our experiments contribute significantly to better understanding the relative importance between isostatic relaxation and emplacement of sills below craters in causing uplift and fracturing of crater floors on earth and other rocky planetary bodies including the Moon.
Publications
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Evidence from the Vredefort Granophyre Dikes points to crustal relaxation following basin-size impact cratering. Icarus, 374, 114812.
Huber, Matthew S.; Kovaleva, Elizaveta; Clark, Martin D.; Riller, Ulrich & Fourie, Francois D.
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Experimental data on Long-term Isostatic Relaxation of Large Terrestrial Impact Structures: Structural Characteristics Inferred from Scaled Analogue Experiments at the UHH-Tec Modelling Lab of the Universität Hamburg. GFZ Data Services.
Eisermann, J. O. & Riller, U.
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Long-term isostatic relaxation of large terrestrial impact structures: structural characteristics inferred from scaled analogue experiments. Earth and Planetary Science Letters, 647, 119029.
Eisermann, Jan Oliver & Riller, Ulrich
